1. Field of the Invention
The present invention relates to an image processing device and a recording medium, and in particular, to an image processing device and a recording medium which enable processing for improving image quality in a digital color image processing, such as reading or copying of a color document, or the like.
2. Description of the Related Art
In recent years, digital color devices have been remarkably developed and spread in the fields of scanners, copying machines, printers, and the like. Further, a document composing environment such as personal computers, word processor softwares, or the like has also advanced and developed. Accordingly, in the field of color image reproduction which uses the above-described digital color devices, not only a natural image of a person, landscape, or the like, but also a document image which is mainly formed by character information, a graph, a diagram, or the like has become an important object of processing.
When the document image is compared to the natural image, characteristically, the document image is expressed by extremely small number of colors, such as from two or three colors to about dozens of colors at most, and a great number of regions having a large surface area and the same color exists in the document image, or the like. As a result, caused by the quality of an original document, by the device characteristics of an image reading device, and by excessive emphasis or the like in an image processing such as gradation correction, MTF correction, or the like, there is a problem in that noise or uneven color is generated in the color region which should be originally the same at the time of image reproduction.
In order to solve the problem, various methods of enhancing the uniformity of a color by using a so-called subtractive color processing technique which reduces the number of colors in an original image have been proposed. For example, Japanese Patent Application Laid-Open (JP-A) No. 8-22532 discloses a technique of reducing unevenness in a document image by limiting a component ratio of colors existing in an original image. Further, JP-A-10-243250 discloses a technique of improving the reproduction of uniform color regions by means of setting a color region which should be reproduced flat and a color region which is not in accordance with a color distribution in an original image and then effecting color correction.